1. Field of the Invention
The present invention relates to a catalyst composition comprising zeolite, alumina, anionic clay, and kaolin, its preparation, and its use in FCC.
2. Prior Art
Environmental concerns have resulted in legislation limiting the sulfur content in fuels, such as gasoline and diesel. Sulfur, when present in gasoline, not only contributes to SOx-emissions, but also poisons car engine exhaust catalysts.
One way of reducing these sulfur levels is hydrotreating. However, such a process requires substantial capital investments and operating costs. It would be more desirable to reduce the sulfur content in situ, i.e. during processing in the FCC-unit.
WO 99/49001 and T. Myrstad et al., Appl. catal. A 187 (1999) 207–212 disclose such an in situ process using a composition comprising a hydrotalcite material impregnated with a metal additive, i.e. a Lewis acid, preferably Zn. According to this document, the impregnated hydrotalcite material can be incorporated into the matrix of an FCC catalyst, or can be used as a separate compound next to an FCC catalyst.
Impregnation generally leads to (a) an inhomogeneous distribution of the metal additive in the hydrotalcite material whereby the metal is mainly deposited on the outer surface of the hydrotalcite particles and/or (b) precipitation of the metal additive as a separate phase next to the hydrotalcite material
The so-obtained metal distribution facilitates leaching of the metal additive into the aqueous suspension containing the other catalyst ingredients during the preparation of the catalyst composition. Such leaching leads to a decrease in metal content of the anionic clays (with consequently a loss in catalytic activity) and may result in precipitation of the metal additive on one of the other catalyst ingredients present in the suspension, e.g. the alumina. The presence of such metal-containing alumina in the catalyst composition can lead to several side reactions (e.g. coke formation) during use in FCC.
During use of the catalyst composition—which consequently leads to abrasion of the catalyst composition—microfines (dust) are formed. If the metal additive is located mainly on the outer surface of the anionic clay phase and/or if the additive is present as a separate phase within the catalyst, the microfines will contain relatively large amounts of the metal additive. This is environmentally undesired, especially when the additive is a heavy metal-containing compound. Furthermore, with the removal of the metal additive from the catalyst, catalytic activity will be lost.